I don't know much, I do know that during the late seventies, GM went to the "tall trim panel. The doors are different too. That is the major change. As for the different trim levels of the trim panels--I don't know.
AFAK, the blazers, subs, and pickups used the same panels. There shouldn't be any changes to the 73/75 blazer's panel even-though the door are cut. Where the doors are cut don't affect the panels although there are caps where the window frame used to be.